CBSE Class 10 Physics Light Reflection and Refraction Assignment Set D

• Light: The natural agent that stimulates sight and makes things visible. Light is reflected from all surfaces.

• Regular reflection takes place when light is incident on smooth, polished and regular surfaces.

• Diffused/irregular reflection takes place from rough surfaces.

• Reflection of Light: Bouncing back of light after striking the surface, in the same medium, is called reflection.

• Types of Reflection:

(i) Regular Reflection: When a narrow beam of light strikes a mirror, the light will not reach your eye unless your eye is positioned at just the right place where the law of reflection is satisfied.
(ii) Diffused or Irregular Reflection: When light is incident upon a rough surface, it is reflected in many directions.

• Two laws of reflection are

• The angle of incidence is equal to the angle of reflection.

• Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.

• Image formed in a plane mirror undergoes lateral inversion.

• Two mirrors inclined to each other give multiple images.

• Beautiful patterns are formed in a kaleidoscope because of multiple reflections.

• Sunlight, called white light, consists of seven colours.

• Splitting of light into its constituent colours is known as dispersion.

• Important parts of the eye are cornea, iris, pupil, lens, retina and optic nerve.

• A normal eye can see nearby and distant objects clearly.

• Visually challenged persons can read and write using Braille system.

• Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.

• Parts of Human Eye:

(i) Cornea: Transparent bulge on the front surface of the eyeball which protects the eye and helps in refraction of light.
(ii) Iris: Coloured diaphragm behind the cornea which controls the amount of light entering the eye.
(iii) Pupil: Dark hole in the middle of iris through which light enters the eye.
(iv) Eye lens: Transparent, crystalline structure behind pupil and iris.
(v) Ciliary muscles: Hole the eye lens in position and control the focal length of the eye lens.
(vi) Retina: Surface of the rear part of the eyeball where the light entering the eye is focused.
(vii) Rods and Cones: Rod cells respond to the brightness of light while cone cells respond to colours.
(viii) Blind spot: It is the least sensitive point where no rodsd and cones are present.
(ix) The space between the cornea and the eye lens is filled with aqueous humour.
(x) The space between the eye lens and the retina is filled with vitreous humour.

Assertion and Reasoning Based Questions

Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.

Question. Assertion : The nature of the image formed by a concave mirror is real and inverted.
Reason : The image formed by a concave mirror depends on the position of the object at infinity.
Answer : (a) 

Question. Assertion : Convex mirror are used for rear view on vehicles.
Reason : The size of the image formed by a convex mirror will be same.
Answer : (b) 

Question. Assertion : A ray of light that travels obliquely from one transparent medium into another will change its direction in the second medium.
Reason : Refraction is due to change in the speed of light as it enters from one transparent medium to another.
Answer : (a) 

Question. Assertion : The refractive index of Kerosene is 1.44 which is optically denser than water.
Reason : The mass density of kerosene is lesser than water.
Answer : (b) 

Question. Assertion : The sequence of rainbow colour is represented as VIBGYOR.
Reason : Formation of VIBGYOR sequence colour is due to the dispersion of white light.
Answer : (a) 

Very Short Answers Type Questions

Question. Where is the image formed when an object is at large distance from a concave mirror ?
Answer : The image formed is at the focus of the mirror.

Question. What kind of image can be obtained on the screen ?
Answer : Real image.

Question. Which metal is the best reflector of light ?
Answer : Silver metal is the best reflector of light.

Question. What is the nature of the image formed by a concave mirror if the magnification produced by the mirror is + 2 ?
Answer : Virtual and erect.

Question. Between which two points of a concave mirror should an object be placed to obtain a magnification of – 2 ?
Answer : Between F and C.

Question. List four characteristics of the images formed by plane mirrors.
Answer :
(a) Size of the image is equal to the size of object.
(b) Formed image is erect.
(c) Image formed by plane mirror is virtual.
(d) Formed image is laterally inverted.

Question. Why is convex mirror used as a rear view mirror in vehicles ? State any one reason. 
Answer : Convex mirror is used as a rear view mirror in vehicles because it gives a wider field view of the approaching traffic.

Question. State two laws of reflection of light. 
Answer : Two laws of reflection of light are :
(a) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
(b) The angle of incidence is equal to the angle of reflection.

Question. Define the term principal axis of a spherical mirror.
Answer : A straight line passing through the pole of spherical mirror and joining it to the centre of curvature of the mirror is known as the principal axis of the spherical mirror.

Short Answer Questions

Question. State two laws of refraction of light.
Answer : Two laws of refraction of light are :
(a) The incident ray, the refracted ray and the normal to the interface of two transparent medium at the point of incidence, all lie in the same plane.
(b) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of medium.

Question. (a) What is an optical medium ?
(b) What do you mean by :
(i) an optically dense medium ?
(ii) an optically rare medium ?
Answer :
(a) A medium through which light can travel is called an optical medium.
(b) (i) While passing from one medium to the other, if the speed of light slows down, then the second medium is said to be optically denser than the first medium.
(ii) While passing from one medium to the other, if the speed of light increases, then the second medium is said to optically rarer than the first medium.

Question. (a) State the two laws of reflection of light.
(b) A light ray is incident normally on a plane mirror. What is its angle of incidence ?
Answer :
(a) The two laws of reflection are :
(i) The incident ray, the reflected ray and the normal at the point of incidence, lie in the same plane.
(ii) The angle of incidence is equal to the angle of reflection (∠i = ∠r).
(b) The angle of incidence will be 0°.

Question. (a) Define lateral shift.
(b) State and explain the factors on which it depends.
Answer :
(a) The perpendicular distance between the path of emergent ray and the direction of incident ray is called lateral shift.
(b) Lateral shift depends on the following factors :
(i) It is directly proportional to the thickness of glass slab.
(ii) It is directly proportional to the angle of incidence.
(iii) It is directly proportional to the refractive index of the glass slab.
(iv) It is inversely proportional to the wavelength of the light used.

Question. Write the relationship between the S.I. unit of the power of a lens and S.I. unit of focal length.
Answer : Reciprocal of focal length of a lens, expressed in metre, is called the power of that lens. Its S.I. unit is 1 dioptre (1 D), where 1 D = 1 m^–1.

HOTS Questions

Question. Amit visited a fair and saw a mirror in which he got a very funny image. The above part of his body was big in size, middle part was of normal size and the lower part of the body showed very small size. What kind of mirror is this?
Answer : Upper part – Concave mirror; Middle part : Plane mirror; Lower part : Convex mirror.

Question. Define the following.
(a) What is ray?
(b) What is beam?
(c) What is reflection of light?
(d) What is reflector?
(e) What is focal length?
(f) What is principal focus?
(g) What is refraction?
(h) What is optically rare medium?
(i) What is optically denser medium?
(j) What is power?
(k) What is 1 dioptre?
Answer : (a) It is the path of light.
(b) Group of parallel light rays emitted by the source of light.
(c) Bouncing back of light after striking any surface.
(d) The surface which reflects the light.
(e) The distance between the pole and the principal focus of the spherical mirror.
(f) A point of the principal axis where the rays of light parallel to principal axis meet.
(g) Bending of light ray when it travels from one medium to another.
(h) When the speed of light is more as compared to other medium.
(i) When the speed of light is less as compared to another medium.
(j) The degree of convergence or divergence of light rays achieved by a lens is expressed in terms of its power
(k) It is the power of lens whose focal length is 1 m.

Question. Write the laws of reflection.
Answer : (a) The angle of incidence is equal to angle of reflection.
(b) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.

Question. Give uses of plane mirror.
Answer : • Looking glass
• Used in submarines
• Solar cooker
• Kaleidoscope

Question. Give uses of concave mirror.
Answer : • Used as reflectors in car headlights, searchlights, etc.
• Used as shaving mirror.
• Used in solar cooker to focus the sunlight on one point.

Question. What are the two types of refractive index? 
Answer : • Relative refractive index– It is the ratio of speed of light in one medium to the speed of light in another medium 
• Absolute refractive index– It is the ratio of light in vacuum to the speed of light in another medium

Question. Name the type of mirror used in the following situations.
(a) Headlights of a car.
(b) Side/rear-view mirror of a vehicle.
(c) Solar furnace.
Answer : (a) Concave mirror
(b) Convex mirror
(c) Concave mirror

Question. Find the focal length of a lens of power –2.0 D. What type of lens is this?
Answer : Given, Power = –2.0
The given lens is concave (power of concave lens is –ve)
P = 1 /f (in metre)
–2.0 = 1/f
f = 1/–2 m
f = – 50 cm
∴ The focal length is – 50 cm.

Case Study Based Questions

1. Read the following and answer any four questions:

Light is a form of energy that produces in us the sensation of sight. Reflection of light is the phenomenon of bouncing back of light in the same medium on striking the surface of any object. The two laws of reflection are the incident ray, the reflected ray and the normal (at the point of incidence), all lie in the same plane and the angle of reflection (r) is always equal to the angle of incidence (i). Refraction of light is the phenomenon of change in the path of light in going from one medium to another.

Question. What is mirage?
(a) Depends on the position of object
(b) Mirror is concave and the lens is convex
(c) Goes straight into the second medium
(d) Optical illusion caused due to total Internal Reflection
Answer : D

Question. What are the two types of mirage?
(a) Thin mirage and thick mirage
(b) Inferior mirage and superior mirage
(c) Intense mirage and diminished mirage
(d) Light mirage and dark mirage
Answer : B

Question. How a mirage is formed?
(a) Between focus and centre of curvature
(b) Is formed away from the normal
(c) Illusion of the presence of water and is a result of refraction of light from a nonuniform medium
(d) Is reflected along the same path
Answer : C

Question. Mirage is observed mainly during ............... days.
(a) Sunny
(b) Winter
(c) Spring
(d) Hot
Answer : A

2. Read the following and anwer any four questions:

Rear view mirror is a device that allows the driver to see rearward. It usually finds its place at the top of windscreen in side the cabin. This device is one of the most basic but essential safety devices in the vehicle. It provides assistance to the driver during overtaking, parking in reverse gear etc. Generally, vehicles also have a pair of mirrors attached to the body from outside. They are popular as ‘side mirrors’ or Outer Rear View Mirrors (ORVM) which serve the same purpose.
Almost all modern cars mount their side mirrors on the doors-normally at A-pillar rather than the wings (the portion of the body above the wheel well).

Question. For a real object, which of the following can produce a real image?
(a) Plane mirror
(b) Concave mirror
(c) Convex mirror
(d) None of these
Answer : B

Question. An object at a distance of +15 cm is slowly moved towards the pole of a convex mirror. The image will get...
(a) shortened and real
(b) enlarged and real
(c) enlarge and virtual
(d) diminished and virtual
Answer : D

Question. A convex mirror is used:
(a) by a dentist
(b) for shaving
(c) as a rear view mirror in vehicles
(d) as a light reflector for obtaining a parallel beam of light
Answer : C

Question. The word ‘AMBULANCE’ is written on the vehicle as:
(a) CNALUBMA
(b) AMBULANCE
(c) ECNALUBMA
(d) None of these
Answer : B

Question. Mark the correct statement:
(a) Convex mirror conform images of objects spread over a large area.
(b) Convex mirrors are used by dentist.
(c) In convex mirror image is formed larger in size, erect and real.
(d) Convex mirror forms real image.
Answer : A

Q1 A ray of light AM is incident on a spherical mirror as shown in the diagram.Redraw the diagram and show the path of reflected ray.

Q2 Explain why a ray of light passing through the centre of curvature of a concave mirror gets reflected along the same path?

Q3 What is the radius of plane mirror?

Q4 Why do we use convex surface for side view mirror?

Q5 Relate the focal length ‘f ‘ and the radius of curvature ‘R’.

Q6 Which kind of mirror is used in the headlights of a motor car and why?

Q7 What is focal length of a plane mirror?

Q8 A concave mirror is placed in water. Will there be any change in the focal length?Give reasons.

Q9 Name the type of mirror which always forms a virtual and diminished image.

Q10 A ray of light LM is incident on a mirror as shown in the figure. The angle of incidence for the ray is the angle between it and the line joining the other points in the figure. Name these two points.

Q15 Name the type of mirror used in:

(a) Solar furnaces

(b) Rear view mirror of a vehicle

(c) Headlights of a car. Support your answer with reason.

Q16 Draw the ray diagram to show

(i) the position

(ii) nature of the image formed when an object is placed between focus F and pole P of a concave mirror.

Q17 A concave mirror and a convex lens are held separately in water. What changes (if any) do you expect in the focal length of either?

Q18 A convex mirror used on an automobile has a focal length of 3m. If a vehicle behind is at a distance of 5m, find the location of the image.

Q19 (i) Distinguish between a real and virtual image.

(ii)Distinguish between a convex and concave mirror.

Q20 We have to form an erect image of an object placed in front of a concave mirror of focal length 15cm. Draw the ray diagram.

Q21 Why does a ray falling normally on a plane mirror, retrace its path?

Please click the below link to access CBSE Class 10 Physics Light Reflection and Refraction Assignment Set D